Printing sleeves are commonly used in a variety of applications, including flexographic and gravure printing. In particular, a printing sleeve that is generally cylindrical in shape can be mounted onto a rotatable printing cylinder for printing images onto a substrate.
A variety of mechanisms can be used to mount the printing sleeve onto the printing cylinder. For instance, xe2x80x9cair-mountingxe2x80x9d is one common way of mounting a printing sleeve. Air-mounting generally refers to the placement of a printing sleeve onto a printing cylinder by supplying pressurized air between the sleeve and the cylinder. Typically, the printing sleeve has an inner surface diameter that is slightly smaller than the outer surface diameter of the printing cylinder. The difference in these diameters is a dimension known as the xe2x80x9cinterference fitxe2x80x9d. Thus, by applying pressurized air, the diameter of the printing sleeve can be slightly expanded so that the sleeve can be mounted onto and/or removed from a printing cylinder.
In some instances, an air-mountable printing sleeve can be formed from multiple concentric layers. In particular, most printing jobs involve an xe2x80x9cimage repeatxe2x80x9d, which is the circumferential length of the image that is to be printed one or more times on a substrate. The circumference of a printing sleeve must be large enough to contain one or more image repeats. Moreover, different printing jobs may involve image repeats that differ in size, and consequently, different printing jobs may require printing sleeve repeats that also differ in size. For instance, a larger sleeve repeat size requires a printing sleeve with a larger circumferences or outer diameter for the same printing cylinder diameter.
To perform a job that requires a larger sleeve repeat size, the outer surface diameter of the printing sleeve must be large enough to yield the larger sleeve repeat size. Thus, printing sleeves resulting from multiple layers are generally used to provide the necessary radial thickness. Specifically, the multi-layer printing sleeves have the effect of increasing the outer diameter of the sleeve to provide a larger repeat size so that the sleeve can be mounted on a smaller diameter printing cylinder that is already available in inventory.
For example, one type of multi-layered sleeve that is currently used in the art includes an innermost core layer that is formed from wound fiberglass coated with epoxy resin. One version of this sleeve contains a bridge layer made from polyurethane (e.g., ISA-PUR 2340) disposed on the outer surface of a core layer. However, this sleeve is generally not capable of being air-mounted onto a cylinder at standard operating pressures (e.g., 80 to 90 psi) unless the thickness of the printing sleeve is less than 0.250 inches. In particular, it was believed that a compressible layer was required to form such air-mountable, multi-layered printing sleeves with a thickness greater than 0.250 inches.
For example, sleeves having a thickness greater than 0.250 inches contain a compressible layer with elastic properties for absorbing radial expansion of the core. The compressible layer is disposed on the outer surface of the core layer and is typically formed from open cell urethanes (e.g., a polyether/polyester polyurethane foam sold as Scotch-Mount(trademark) 4032 by Minnesota Mining and Manufacturing Company) or a rubber material. In general, the compressible layer usually has a thickness between 0.0030 to 0.250 inches.
In addition to the above layers, the prior art multi-layered sleeve also contains one or more layers that add thickness to the sleeve. For example, materials such as rigid polyurethane foam or other forms of polyurethane (e.g., ISA-PUR 2330 and ISA-PUR 2340 which are sold by H.B. Fuller Austria, NOMEX(copyright) which is sold by DUPONT, and honeycomb structures) are utilized by the prior art sleeve. The thickness of such layers varies depending on the particular image repeat utilized, but is typically less than 3 inches. In addition, other outer layers are also sometimes disposed on the outer surface of these layers.
However, one problem associated with such multi-layered printing sleeves is that the compressible layer of the sleeves tends to disintegrate after a period of time. Specifically, as the sleeve is used to impart an image onto a substrate for a period of about 1 to 2 years, the open cell structure of a polyether polyurethane foam layer, for example, gradually becomes destroyed. As a result, the tolerance (or roundness) of the outermost surface of the sleeve decreases. In particular, the xe2x80x9cTotal Indicated Runoutxe2x80x9d (TIR) often increases to greater than 0.001 inches, which causes the sleeve to be ill-suited for most printing applications. Thus, when the compressible layer is destroyed, current sleeve users or xe2x80x9cconvertersxe2x80x9d must replace these damaged sleeves with new and expensive sleeves.
As such, a need currently exists for an improved multi-layered printing sleeve that is capable of being air-mounted onto a printing cylinder.
The present invention is generally directed to a printing sleeve for use in flexographic or gravure printing applications. In particular, a printing sleeve of the present invention contains a bridge layer that is formed from a generally rigid and relatively expandable material, which is disposed adjacent to a core layer.
In general, the printing sleeve includes a core layer that is generally cylindrical in shape and that constitutes the innermost portion of the printing sleeve. In some embodiments, the core layer of the printing sleeve is formed of an expandable, high rigidity material. Some examples of compositions that are suitable for use in the core layer include, but are not limited to, aramid fiber bonded with epoxy resin or polyester resin; reinforced polymeric material such as hardened glass fiber bonded with epoxy resin or polyester resin, the latter two also known as fiberglass reinforced epoxy resin or fiberglass reinforced polyester; DUPONT(copyright) MYLAR(copyright) or tri-laminate KEVLAR(copyright); carbon-reinforced epoxy resin; nickel; copper; and the like. The radial thickness of the core layer can, in some embodiments, be between about 0.020 to about 0.100 inches, with the larger thickness being used for sleeves with greater diameters and/or axial lengths.
As stated, a printing sleeve of the present invention also includes a generally cylindrical bridge layer. The bridge layer can be made from a generally rigid, relatively expandable material. As used herein, the phrase xe2x80x9crigidxe2x80x9d refers to a material having a certain Shore hardness. In some embodiments, for example, the bridge layer can be made from a material having a Shore D hardness of about 20 to about 85, and in some embodiments, from about 45 to about 50. In one particular embodiment, for example, the bridge layer can contain a polyurethane material having a Shore D hardness between about 45 to about 50. One such polyurethane material may be obtained from H.B. Fuller Austria under the tradename ISA-PUR 2330.
Besides being generally rigid, the bridge layer, as stated above, can also be relatively expandable. As used herein, the term xe2x80x9cexpandablexe2x80x9d refers to a material that can expand a certain radial distance upon the application of air at a certain pressure. For example, at air pressures between about 80 to about 90 psi, the printing sleeves typically expand in a radial direction between about 0.0015 to about 0.0045 inches, and in some embodiments, between about 0.0025 to about 0.0035 inches. For example, in one embodiment, a printing sleeve having a diameter less than 7 inches expands, in a radial direction, about 0.0025 inches. Moreover, in another embodiment, a printing sleeve having an inner diameter greater than 7 inches expands, in a radial direction, about 0.0035 inches.
The thickness of the bridge layer can generally vary. In most embodiments, for example, the thickness of the bridge layer is between about 0.125 to about 1.50 inches, and in some embodiments, between about 0.125 inches to about 1.00 inches.
Moreover, the printing sleeve can also contain one or more outer layers disposed on the outer surface of the bridge layer. The outer layer(s) can be used to add further thickness to the sleeve and/or as a cover layer for the sleeve. In general, any number, size, shape, and/or type of outer layers can be used in the present invention, so long as the resulting printing sleeve can be air-mounted onto a printing cylinder. For example, some suitable materials that can be utilized in forming an outer layer include, but are not limited to, aramid fiber bonded with epoxy resin or polyester resin; reinforced polymeric material such as hardened glass fiber bonded with epoxy resin or polyester resin, the latter two also known as fiberglass reinforced epoxy resin or fiberglass reinforced polyester; DUPONT(copyright) MYLAR(copyright) or tri-laminate KEVLAR(copyright); a polyurethane material (e.g., ISA-PUR 2330 or ISA-PUR 2340 from H.B. Fuller Austria under the tradename ISA-PUR 2330); elastomeric rubber materials; elastomeric polyurethane materials; polyurethane expanded foam; open cell polyurethane foam; nickel; copper; carbon-reinforced epoxy resin; and the like. In some embodiments, a metal outer layer, such as an aluminum extruded layer, can also be pressed onto the bridge layer.
Further, the outer layer(s) can also be made from a rigid material or non-rigid material. For instance, in one embodiment, an outer layer can be made from a polyurethane material having a Shore D hardness from about 75 to about 85. In addition, the outer layer(s) can also have any desired thickness, so long as the overall thickness of the printing sleeve is greater than about 0.250 inches. For example, in one embodiment, an outer layer has a thickness greater than about 0.050 inches, in some embodiments between about 0.065 to about 0.250 inches, and in some embodiments, between about 0.075 to about 0.200 inches.
As a result of the present invention, printing sleeves can be formed without a compressible layer disposed adjacent to the outer surface of a core layer. By eliminating such a compressible layer, the printing sleeves of the present invention are believed to be more durable and maintain better TIR tolerances than conventional printing sleeves. In particular, a generally rigid bridge layer that can expand during mounting and demounting can provide the printing sleeve with durable properties.
Other features and aspects of the present invention are discussed in greater detail below.